The functionality and performance of conventional digital cameras are often limited by the photo-electronic sensor and optical technologies used to capture two-dimensional planar images of 3D scene. The flat sensor array is composed of numerous single-sized, rectangular shaped, and uniformly distributed light sensing elements fabricated on a rigid silicon substrate using very-large scaled integration (VLSI) design processes. Complex and heavy optical assemblies comprised of specialized lens and mirrors are often required to enable images with a wide filed-of-view (FOV) to be captured. An illustration of a specialty lens is a wide-angle “fish-eye” lens (U.S. Pat. No. 6,304,285B1 and U.S. Pat. No. 4,647,161). However, optical solutions for enlarging the FOV often lead to significant image distortion which must be corrected by sophisticated computational algorithms.
The limited FOV provided by commercially available digital sensors has been increased by implementing an active pan-tilt platform that dynamically repositions the sensor about the center of projection (U.S. Pat. No. 5,627,616). The speed in which the camera can be reoriented during data acquisition has greatly reduced the effectiveness these systems. An alternative approach to creating a wide FOV involves numerous cameras pointing in different directions (U.S. Pat. No. 5,920,337). However, it is difficult to seamlessly register and integrate multiple views because the constituent images are produced by unique cameras with different centers of projection. This technology is difficult to calibrate, prone to alignment errors and requires significant hardware for a full 360° view.
The physical restrictions and limited performance capability of silicon-based technologies have prompted researchers to look at biological materials as a means of improving detector characteristics, and simplifying the design and fabrication of non-traditional imaging systems. Biomaterials such as; bacteriorhodopsin (bR) exhibit photoresponse characteristics similar to the rhodopsin found in mammalian vision systems including high sensitivity and large dynamic range. Bacteriorhodopsin is the light-harvesting protein present in the plasma membrane of Halobacterium salinarium. Under anaerobic conditions the bacterium's membrane grows purple membrane (PM) patches in the form of a hexagonal two-dimensional crystalline lattice of uniformly oriented bR trimers. It is the crystalline structure that provides bR with chemical and thermal stability thereby making it a useful material for developing artificial vision systems.
A number of different photosensitive devices have been created by immobilizing PM patches onto a rigid substrate such as silica glass coated by conductive tin or indium tin oxides, and metal electrodes such as gold and platinum (J.P. Pat. No. 04006420A2 and U.S. Pat. No. 5,260,559). In this context, a 16×16 pixel array of bR photocells was fabricated on the conductive solid substrate for image detection (U.S. Pat. No. 5,260,559 and U.S. Pat. No. 6,977,160). The differential response exhibited by each bR photocell in the spatial array provided the necessary photoelectric signal for motion detection. Similarly, a position-sensitive motion sensor using the image-recording capability of bR at high pH was patented (J.P. Pat. No. 06235606A2). Recently, the gate terminal of a GaAs-based MOSFET and nano-black lipid membranes (J. Xu et al., 2004, C. Horn and C. Steinem, 2005) has been explored as a viable; technology for micro and nano applications.
A color sensor that consisted of a blue-, green-, and red-sensitive chromoprotein thin films was developed (J.P. Pat. No. 03237769A2). Furthermore, a dynamic adaptive camouflage system was created by mounting the bR photodetectors and display devices on an apparatus and displaying a spatially shifted image of the incident ambient light (U.S. Pat. No. 5,438,192).
It would be very advantageous to provide single and multi-spectral bioelectronic sensing technology fabricated on bendable or flexible plastic substrates. The direct deposit of photosensitive materials onto low-cost flexible printed electronic circuits would enable design engineers to create innovative lightweight, durable and non-planar image sensing systems for example, such as spherical or omni-directional photodetector array based on bR films can be used in a variety of imaging applications including motion detection, robotic and vehicle navigation. It would be very beneficial to develop photo-responsive sensors that can be adhered permanently to non-planar customized surfaces.